新疆达尔布特蛇绿混杂岩带硅质岩地球化学及沉积环境  

Geochemical Characteristics and Depositional Environment of the Silicalite from the Darbut Phiolitic Mélange Zone in North Xinjiang

作　　者：张丽敏[1] 李永军[1] 向坤鹏[1] 孙勇[1] 王军年[2] 

机构地区：[1]长安大学地球科学与资源学院,西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [2]新疆地质矿产勘查开发局地质七队,新疆乌苏833000

出　　处：《西北地质》2016年第2期70-83,共14页Northwestern Geology

基　　金：中央高校基金“萨尔托海蛇绿岩铂族元素地球化学研究”(310827161020)

摘　　要：西准噶尔达尔布特晚古生代硅质岩一般呈薄层状覆盖在蛇绿岩之上,为探讨其物源和沉积环境,对达尔布特多条蛇绿混杂岩剖面中的硅质岩进行了岩相学和地球化学研究,结果表明其要为紫红色和灰白色,主要由微晶自生石英和隐晶组成,可分为生物化学成因硅质岩和有火山凝灰质加入的硅质岩两类,可能部分样品存在二者之间的过渡。前者以高Si、Fe,低Al、Ti等为特征,且稀土总量低,部分样品Ce负异常明显,部分有微弱正异常,微量元素含量也很低;后者一般以高Si、Al、Ti,低Fe等为特征,具酸性火山物质加入趋势。综合认为,该区硅质岩产于边缘洋盆环境而非大洋环境。这与前人关于达尔布特蛇绿岩形成于SSZ构造环境的观点是一致的,具有重要的构造环境指示意义。Thelate Paleozoic silicalitesare covered the ophiolites with thin layered shape,which is generally and often transformed into lenticular structurein oceanic subduction and tectonic emplacement process in Darbut,West Junggar.In order to explore the provenance and sedimentary environment,the petrography and geochemistry studiesabout these silicalitesfrom the cross section of the Darbut ophiolites have been carried out in this paper.The results show that these silicalitesmainly show purple and gray color,which arecomposed of microcrystal authigenic quartzsand cryptocrystals.And the microcrystal authigenic quartzs arevisible observed by microscope.According to the whole rock geochemical characteristics,these silicalites can be divided in biochemistry silicalites and siliceous rocks with volcano tuff,with some of them have the transitioncharacteristics of both two types.The biochemistry silicalites generally have high Si and Fe contents,low Al,Ti and total REE values,with low contents of trace elements,some of them show negative Ce anomalies,and part of them have weak even positive Ce anomalies.The siliceous rocks with volcano tuffare generally charactered by high Si,Al,Ti contents,low Fe value,with obvious increasing trend of acidic volcano material components.Integrating the geological occurrence,petrography and geochemical characteristics,it is believed that these silicalites are formed in marginal ocean basin rather than open oceanic environment.This result is agreed with the SSZ settings of previous study,having important significance to recognize the tectonic environment of the ophiolite.

关 键 词：硅质岩 地球化学 边缘洋盆 达尔布特 西准噶尔 

分 类 号：P588.3[天文地球—岩石学] P59[天文地球—地质学]